There is an urgent need to process specific industrial or agricultural effluents (such as olive mills, wineries, piggeries, soy or coffee bean industries) that are unsuitable for discharge into standard sewage treatment plants due to the large amounts of organic and suspended matter. The disposal of such effluents without any treatment is known to cause serious environmental problems. Wineries are major producers of organically laden wastewater, yielding about 1000-3000 L per ton of grapes characterized by high contents of organic material and nutrients, high acidity, and large variations in seasonal flow production. The very high values of organic matter, suspended solids, and sodium adsorption ratio (SAR) make such water inadequate for disposal in common sewage systems.
Colloidal particles that tend to clog filtering devices are one of the problems with such effluents. In most cases, colloidal stability (i.e., colloids' tendency to remain dispersed) in organically loaded effluents is due to three effects: (a) small particle size, yielding large hydrodynamic friction forces: (b) electrostatic repulsion due to similar charges of the effluent's colloids, which keep the particles in suspension, and (c) the density of the organic colloids, which is close to that of water and, therefore, even if a large neutral particle forms, its sinking velocity will be very slow. In wastewater, colloid removal is crucial to avoiding clogging of aerobic or anaerobic digesters. In several cases, pretreatment processes in wastewater involve use of chemicals for the neutralization, flocculation, and precipitation of those colloids. The first step in this process is a stage technically known as ‘coagulation’, defined as neutralization of the colloids' charge, thereby reducing electrostatic repulsion between them and enabling their aggregation. In some cases, this process is followed by ‘flocculation’, in which bridging compounds are used to form chemically bonded links between the neutral colloidal particles, enmeshing them into relatively larger aggregates that, due to their size and density, sink at the bottom of the vessel, leaving a clarified effluent.
Such destabilization of the colloidal suspension, inducing flocculation of large amount of suspended matter, lowers values of total suspended solids (TSS), turbidity, and even the chemical oxygen demand (COD). This, in turn, improves the efficiency of following water treatments, thereby reducing environmental hazard.
Clays and organoclays (clay minerals treated with organocations) have been widely used for the pretreatment of effluents. Combination of clay minerals and organic compounds efficiently removed colloidal solids in paper mill wastewater. Cationic or anionic polyelectrolytes, combinations of coagulants and polyelectrolytes, or even combination of clay minerals and organic quaternary ammonium ions have been used for the removal of organic contaminants from olive mill wastewater. In all cases, considerable changes in the colloidal properties of the effluent, including reduction in turbidity, TSS, COD and other quality parameters were achieved.
U.S. Pat. No. 6,447,686 discloses a high speed coagulant-flocculant and sedimentation method for treating wastewater. The method is based on an arrangement of tanks comprising a mixing tank, an agitating tank, a polymer aggregation tank and a sedimentation tank successively connected, wherein the mixing tank comprises an aggregating agent which is based on clay minerals.
The term “nanoparticle” is usually used for a combined material which has at least on one dimension a size of 100 nm or less. Thus, most clay minerals are considered nanoparticles. The use of clays as building-blocks for assembling organic species at the nanometer range yields useful hybrid nanostructured materials. Nanocomposite materials consisting of polymer molecules and natural or layered minerals like clays can be prepared and designed by the combination of clay minerals with organic polymers interacting at the molecular level (Ruiz-Hitzky, 2001).
In previous studies, we demonstrated the ability of suitable nanoparticles for very efficient removal of phenolic compounds similar to components of olive mill or winery wastewater (Rytwo et al., 2007). Other studies (Rytwo et al., 2011) presented a very effective pretreatment of effluents based on combination of organoclay nanoparticles and crude clay, which changed the colloidal stability of winery and pickle industry effluents, reducing TSS and turbidity for several cycles by means of a two-step process: a first step performed with an organoclay, and a second step performed by adding raw clay. In general, Rytwo et al (2011) process was similar to that used nowadays in the industry: (a) a coagulation step, performed in industry with cationic polymers, or with aluminium sulphate or other inorganic polycations (in Rytwo et al, 2011, the coagulant was based on an organoclay), and (b) a flocculation step performed in the industry with flocculants in several cases based on cationic or anionic polyacrylamide derivatives (in Rytwo et al, 2011, the flocculant was a raw clay mineral).
PCT Publication WO 2012/176190 of the same applicant discloses a one-step method for pretreatment of wastewater or recreational water with a high organic load using nanocomposites consisting of an anchoring particle and a polymer.